Measuring Nanoparticle Exposure - Application Note NSAM-001 - TSI

compared with the Model 3550 reading averaged over the entire period of SMPS sampling. They must be
within ±10% (for TB and A) for the Model 3550 to pass calibration and verification testing.
Applications
The Model 3550 provides a simple and fast solution for indicating the surface area equivalent dose of
particles in the size range of 10 to 1000 nanometers. The Model 3550 is well suited for the following
applications:
• Monitoring workplace exposure to nanoparticles
o Industrial hygiene surveys
o Ambient work area monitoring
o Baseline screening and trending
o Engineering studies
• Material science and production process monitoring
• Inhalation toxicology research studies
• Epidemiology research studies
Theory of Operation
The Model 3550 is based on diffusion charging of sampled particles, followed by detection of the charged
aerosol using an electrometer. An aerosol sample is drawn into the instrument continuously at a rate of
2.5 L/min. The flow is split with 1 L/min passing through two filters (a carbon and a HEPA) and an ionizer
and 1.5 L/min of aerosol sample flow.
The flow streams are merged in a mixing chamber where particles in the aerosol flow mix with the ions
carried by the filtered clean air. This patented counter-flow diffusion charging ** brings the aerosol particles
into a defined, charged state. The separation of particles from direct interaction with the corona needle
and/or the strong field near it reduces particle loss and makes the charging process more efficient and
reproducible. The charged aerosol then passes through an ion trap to remove excess ions and charged
aerosol. The aerosol then moves on to an electrometer for charge measurement. In the electrometer,
current is passed from the particles to a conductive filter and measured by a very sensitive amplifier. A
microprocessor controls the instrument flows and measures various operational parameters and converts
the measurement output into units of square micrometers per cubic centimeter (µm 2 /cc 3 ).
** U.S. Patent No. 6,544,484
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